27 May
2003
27 May
'03
11:09 a.m.
(the section
in 'The Art of=20
Electronics' 2nd edition is a good staring point),=20
Unfortunately I
don't own this book. When I tried to order it from .de,
the cost was prohibitive.=20 and these DEC PSU=20
bricks are a pretty standard step-down regualtor circuit.
Well, it looks like the
H7441 has some funky design tricks.=20 The only unconvention feature is that the
controller is=20
a 723 chip, not a special SMPSU chip.=20
The H745 has a 723, the H7441 has two
OPAs and two NE555. The H745 looks
quite simple and I think I understand what the different parts do, but
the H7441??? One OPA seams to do some over current protection, one the
voltage regulation. So the NE555 are doing the ON / OFF timing??? Have
to dig deeper into that...=20
Unfortunately it doesn't seam as simple as the SGI Indigo2 PSU repair I
did today. I had a close look at the PCBs of the PSU and saw
electrolyte... The machine seams to run stable again, now that I
As I said, most SMPSU faults are capacitors or power transistors :-)
replaced the electrolyte capacitor in question. :-)=20
-tony